The Football Association disciplinary panel that banned Chelsea's captain John Terry for racially abusing the Queens Park Rangers defender Anton Ferdinand found the defence he maintained for a year "improbable, implausible and contrived", it emerged on Friday.

Even as hopes were expressed that the verdict would draw a line under a damaging year-long saga that led to Terry's international retirement and the resignation of Fabio Capello as the England manager, Ashley Cole sparked new controversy by branding the FA a "bunch of twats".

In a 63-page ruling, the FA regulatory commission found there was "no credible basis" for Terry's defence that he was merely repeating back to Ferdinand in indignation the phrase "fucking black cunt" in the belief that the QPR player had accused him of racial abuse. It also cast serious doubt on the evidence of Cole and the "materially defective" recollections of the Chelsea secretary, David Barnard. The ruling suggested that Cole's evidence "evolved" over time to suit the case that Ferdinand may have said the phrase in question on the pitch.

The Chelsea left-back, who is due to win his 100th England cap a week on Tuesday against Poland, said via Twitter after seeing news of the verdict on television: "Hahahahaa, well done #fa I lied did I, #BUNCHOFTWATS." He apologised two hours later via his solicitor, claiming the remarks were made "in the heat of the moment". The tweet was sent just as Roberto Di Matteo was giving a press conference and the Chelsea manager was forced to insist his players were not "out of control".

It is understood that the England manager, Roy Hodgson, called Cole and the FA later confirmed he would join up with the squad as planned on Monday.

Terry was cleared by a court in July of a racially aggravated public order offence, although the magistrate cast doubt on his version of events. He was then found guilty of misconduct by the FA last month and handed a four-match ban and a £220,000 fine. Whereas the criminal case had to be proved beyond reasonable doubt, the FA commission made its judgment on the balance of probabilities. Terry has until 18 October to decide whether to appeal and Chelsea refused to comment further while that possibility remained active.

"The commission is quite satisfied, on the balance of probabilities, that there is no credible basis for Terry's defence [in using the phrase]," the ruling said.

The three-strong FA commission heard evidence from Ferdinand but not from Terry or Cole, who declined to appear. It was forced to rely on their evidence at Westminster magistrates court.

The verdict also reiterated that it was not the panel's job to rule on whether Terry was a racist or not: "In common with the Crown's proceedings, the FA's case is that Mr Terry said the words by way of an insult to Mr Ferdinand. It is not the FA's case that Mr Terry is a racist."

The saga, which along with last season's incident involving Luis Suárez and Patrice Evra sparked fevered debate about the prevalence of racism in the game, began during an ill-tempered televised match between QPR and Chelsea on 23 October last year. The FA argued it could not hear the case until after the criminal proceedings, which ended with Terry's acquittal in July.

According to "cogent" new evidence considered by the panel but not by the court, in an interview with FA officials at Chelsea's training ground five days after the match, Cole said he heard a "b-word" but did not mention the word black. In a later emailed statement, Cole said the word "could have been Bridge". But Barnard later emailed the FA after discussing the matter with Cole to add the words "black or Bridge".

In his witness statement some 10 months later Barnard also claims that Cole heard the word "cunt" being used in close proximity to the "b-word". But the commission found on the balance of probabilities that Cole's original evidence contained neither that word nor "fucking" – the "unholy trinity" of words that Terry claimed had provoked his outburst.

"All of this causes the commission to have very real concerns about the accuracy of Mr Barnard's recollection, and the motivation for the assertions that he makes in his witness statement about what Mr Cole said during the FA interview." The commission said those concerns raised "significant doubts" about the case that Barnard advances.

In deciding the punishment, the commission took into account Ferdinand's victim impact statement that made plain he had been "badly affected" by the incident, and the high-profile nature of the match. Weighed against that was the fact the insult was said only once and testimonials in favour of Terry from team-mates and others in the game.

Kick It Out, the campaign group that has done much to help rid football grounds of racism over the past two decades, said the episode had threatened to undo that good work. A spokesman said: "It's a period that has polarised the game, undermined the good work being done at all levels, and it must never be allowed to happen again."

Chelsea are likely to take disciplinary action against Cole over the language in his tweet but stated that "Ashley co-operated at all times with the FA and stands by the evidence that he gave and does not accept the criticism that has been made".

The commission said that the "highly material issues" raised by Barnard's email and Cole's evidence were not considered by the magistrate in the criminal case, although it is understood they were supplied to the Crown Prosecution Service by the FA.

"Had it been before him, the commission has no doubt that the chief magistrate would have examined Mr Cole's evidence as to what he claims he heard Mr Ferdinand say to Mr Terry on the pitch very carefully indeed, or scrutinised it even more closely than he may have done," it said.